The present invention relates to a novel sintered body suitable for use as a refractory or abrasive material with its high mechanical strengths at elevated temperatures.
In the prior art, various kinds of sintered bodies are employed for manufacturing certain structural materials suitable for use for rocket housings, turbine blades, high-speed cutting tools and the like, in which high mechanical strengths, e.g. flexural strength and hardness, are essential even at extremely high temperatures. As is well known, a class of such sintered bodies is composed of titanium diboride (TiB.sub.2) as the basic component utilizing its high melting point, hardness and mechanical strengths at elevated temperatures. These TiB.sub.2 -based sintered bodies are usually prepared by sintering a binary powder mixture composed of TiB.sub.2 as the main component and a second component including a powder of a metal such as chromium, molybdenum, rhenium and the like, a metal diboride such as chromium diboride (CrB.sub.2), Zirconium diboride (ZrB.sub.2) and the like, and a nickel phosphide or a nickel-phosphorus alloy (hereinafter denoted as Ni.P).
The above described binary sintered bodies, however, have their respective drawbacks in their performance as well as in their preparation. For example, an extremely high sintering temperature of 2000.degree. C. or higher is required for the sintering of the TiB.sub.2 -metal, e.g. TiB.sub.2 -chromium, TiB.sub.2 -molybdenum and TiB.sub.2 -rhenium, binary sintered bodies giving rise to a very hard difficulty in the production of industrial scale. In addition, these TiB.sub.2 -metal binary sintered bodies suffer from their relatively low flexural strengths in the range of, for example, 40-50 kg/mm.sup.2. The TiB.sub.2 -metal diboride, e.g. TiB.sub.2 -chromium diboride and TiB.sub.2 -zirconium diboride, binary sintered bodies are also subject to the drawbacks of the high sintering temperature and the relatively low flexural strength along with the low relative density, i.e. the ratio of the apparent density to the true density of the sintered body.
The sintering temperature of the TiB.sub.2 -Ni.P binary sintered body, on the other hand, may be as low as ranging from 1000.degree. to 1600.degree. C. and a satisfactorily high flexural strength of around 100 kg/mm.sup.2 is readily obtained with these binary sintered bodies (see, for example, Japanese Patent Disclosure No. SHO 52-106306). The binary sintered bodies of this class have, however, rather poor heat resistance and cannot be used at a temperature exceeding the melting point of the Ni.P, viz. 890.degree. C.
Thus, there have hitherto been known no satisfactory refractory or abrasive material which is a high-density, high-strength and heat-resistant sintered body of TiB.sub.2 as the main component easily manufactured even with a not excessively high sintering temperature.